1. Field of the Invention
The present invention relates to a common mode choke coil for suppressing common mode noise.
2. Description of Related Art
A common mode choke coil can be composed of at least two coil portions, but in order to improve the amount of attenuation to suppress common mode noise, to reduce the size and the thickness, or to add a protection function, a common mode choke coil composed of a combination of many more coils is used (JP 2013-12702A). As shown in FIG. 14, a common mode choke coil 10 includes a first coil portion 11 and a second coil portion 12 that are connected to each other in series between a first terminal T1 and a second terminal T2 provided on a first transmission line of two balanced lines connecting from a power source to a load, and a third coil portion 13 and a fourth coil portion 14 that are connected to each other in series between a third terminal T3 and a fourth terminal T4 provided on a second transmission line of the two balanced lines. Each coil portion is produced by a conducting wire being spirally wound around an annular ferrite core.
Here, the first coil portion 11 and the second coil portion 12 are wound in mutually opposite directions, and the third coil portion 13 and the fourth coil portion 14 are also wound in mutually opposite directions. Also, the first coil portion 11 and the third coil portion 13 are wound in mutually opposite directions, and the second coil portion 12 and the fourth coil portion 14 are also wound in mutually opposite directions.
In the common mode choke coil, magnetic saturation of the cores caused by the magnetic force generated by load current can be suppressed by bringing the coupling factor between the two coil portions of the first transmission line and the two coil portions of the second transmission line of a magnetic circuit constituted by the four coil portions closer to 1 while ensuring high electric insulation property (voltage resistance characteristics) between the two coil portions of the first transmission line and the two coil portions of the second transmission line, and thus an even higher inductance value can be ensured, and common mode noise flowing toward the power source side can be suppressed more effectively. In addition, if it is unnecessary to increase the inductance value, the reduction in size and weight can be achieved, and it is possible to suppress a set mounting space in which the common mode choke coil is to be mounted, and simplify the attachment structure. It is also thereby possible to reduce the cost of the common mode choke coil and the mounting set.
With the common mode choke coil 10, the four coil portions 11, 12, 13 and 14 are each housed in a case-like bobbin made of an insulating resin, and thereby four independent coil elements are produced. The four coil elements are engaged to each other, and thereby the unitary common mode choke coil 10 having four terminals is assembled.
However, in the conventional common mode choke coil 10, the four coil portions 11, 12, 13 and 14 are respectively disposed in four quadrants of an orthogonal coordinate system in the order of the first quadrant, the second quadrant, the fourth quadrant and the third quadrant so as to be as close to each other as possible (not shown) such that the first coil portion 11 of the first transmission line and the third coil portion 13 of the second transmission line are brought closer to each other while ensuring an insulation distance, and also that the second coil portion 12 of the first transmission line and the second coil portion 14 of the second transmission line are brought closer to each other while ensuring the insulation distance so as to increase the coupling factor while obtaining electric insulation property between the first transmission line and the second transmission line. However, the common mode choke coil 10 is problematic in that the coupling factor is still as low as about 0.94 to 0.96 due to the spatial distance between coil portions being large.
In addition, in the manufacturing process of the conventional common mode choke coil 10, the four coil portions 11, 12, 13 and 14 are respectively housed in four bobbins to produce four coil elements, and thereafter in a state in which the four coil elements are respectively disposed in four quadrants of an orthogonal coordinate system in the order of the first quadrant, the second quadrant, the fourth quadrant and the third quadrant, it is necessary to perform an operation of causing an annular core to pass through the inner spaces of the four coil portions and bundling the coil elements together by using some kind of clamping member. Accordingly, positioning of the coil elements becomes unstable and inaccurate, as a result of which fixing of the coil elements with the use of a clamping member becomes unstable, which requires an additional need to use a molded structure for fixing the coil elements, and causes many problems such as the assembling operation being complex and inaccurate, and an additional component being required as a countermeasure, which results in a squeeze on the cost.